The irony of the spectacular failure to recall Wisconsin Gov. Scott Walker in Tuesday’s special election was this: It was even more spectacular because it was so utterly predictable.

Walker had led in the polls for months, and at or above 50 percent. Even more telling were actual electoral results in Wisconsin over the past 16 months — results that followed the eruption of the civil war in the state between Walker and the public-sector unions whose power over state government he’d curbed.

In an April 2011 dry run of Tuesday’s race, exactly the same anti-Walker forces had sought to oust a conservative state Supreme Court justice in a special election — and failed to pull it off.

Later that year, various recall efforts against state senators failed to wrest control of Wisconsin’s Legislature from the GOP.

And in the April primary, conducted to select a Democrat to challenge Walker, 640,000 fired-up Republicans came out to the polls nonetheless to cast a vote for their embattled governor — a sign of voter commitment that should’ve made it clear to the forces of recall just what an uphill climb they had.

And yet liberals still managed to look, talk and sound utterly gobsmacked on Tuesday night. And to act like — there is no other word for it — fools.

A little later, after the victory was assured, Schultz was emotionally prostrate. “How could this happen?” he demanded before asserting with no evidence that Walker “could be indicted” within days.

Finally, he stared into the camera and offered these words of wisdom: “It’s a tough one to take, but it’s about being in the fight. It’s about believing what you believe in and sticking to your guns and not giving up. There’s no shame, there’s no embarrassment in the way this has been played out in Wisconsin.”

No, there’s only shame and embarrassment in the way this played out on MSNBC.

It wasn’t just chat-show folks who made asses of themselves. You’d think experienced political professionals would know better than to place their trust in exit polls, notoriously inaccurate surveys that had John Kerry winning the 2004 election by five points when he actually lost by three.

Yet there was David Axelrod — David Axelrod! President Obama’s chief campaign strategist! — popping up on Twitter 90 minutes before the polls closed, armed with the false knowledge that the same exits which falsely portrayed a tight race between Walker and his opponent also showed Obama winning big against Romney in Wisconsin.

And so Axelrod offered a pithy Tweet in the hilariously ignoble tradition of the 1948 “Dewey Defeats Truman” headline: “Bad night in Boston,” he wrote. “Wisconsin raises big questions for Mitt.”

Yeesh.

If one were to similarly extrapolate from highly problematic data in similar fashion, one might say the only big question Wisconsin actually raised for Mitt was what color drapes he would prefer in the Oval Office.

The point isn’t that Walker couldn’t have lost, but that his defeat was highly unlikely, and the evidence it might happen highly questionable. So why was the snake oil so quickly and easily swallowed?

You might just as easily ask why it was that Obama and the Democrats simply refused to heed the meaning of the solid GOP bloc against the massive and wasteful stimulus in 2009 — and in forcing through that ineffectual monstrosity, effectively created the citizens’ movement called the Tea Party.

Or why they refused to heed the message sent at the start of 2010 by the surprise victory of Scott Brown in the special election in Massachusetts and instead went on to muscle ObamaCare into law — giving the Tea Party renewed passion and setting up the historic 63-seat “shellacking” in the 2010 midterm election.

Or why they came to believe that the ragtag band of anarchists and shiftless hippy-wannabes that made up the “Occupy” movement were going to change the world.

Why? Because they don’t only sell the snake oil, they drink it themselves. They buy their own propaganda; they believe the hype.

Their vanity is their gravest weakness — and the secret weapon in the Republican arsenal.